This invention relates generally to hermetic refrigeration compressors of the type used in household appliances, and more particularly, to a suction muffler and cylinder head arrangements for single reciprocating piston compressors.
Refrigeration compressors used for household appliances such as refrigerators and freezers are generally of low horsepower, usually less than one third horsepower at the most and ranging down to as little as one sixth horsepower. Such compressors, when of the single piston type, use a relatively small displacement cylinder running at a relatively high speed powered by a two-pole electric motor which results in a maximum speed of 3,450 rpm using a 60 hertz power supply. Such compressors are generally run on a high-duty cycle which may range from 50 to 90%, depending upon the load inside the appliance and the ambient temperature. The application of such compressors requires that they have an extremely long life and must operate at a very low noise level and a very high efficiency for purposes of energy conservation.
Because of the relatively small displacement of such compressors, their valve arrangement is usually a valve plate mounted on the end of the cylinder utilizing a single-valve port for the suction side and single discharge port. Thus, the suction port operates with a reed valve formed out of a sheet of spring material on the underside of the valve plate and the discharge port is sealed off by a reed discharge valve mounted on the outer side of the valve plate. The valve plate is then covered by a cylinder head having suction and discharge plenum chambers formed therein with a conduit leading from the discharge plenum chamber to an external muffler, likewise, the suction plenum has a conduit leading from a suction muffler remote from the cylinder head and generally positioned to receive the incoming or return refrigerant gas in such a manner as to permit a minimum heating of the return gas by the environment within the compressor shell.
The cylinder head must be designed with the discharge plenum large enough to contain the discharge valve assembly and allow flow of the compressed refrigerant with a minimum of restriction. Because the compressed gas now has a high temperature, it tends to heat the surrounding environment and cylinder head. Because of the pressures within the discharge plenum, it is generally necessary to make the cylinder head from a metal casting using such materials as cast iron, or aluminum which tend to readily conduct the heat from the discharge plenum throughout the full extent of the cylinder head so that the entire cylinder head tends to be raised to the temperature of the discharged gases. Generally, the two plenum chambers in the cylinder head are divided by a wall which is preferably made as thin as possible to allow a maximum plenum volume in the small amount of space available.
On the other hand, the suction plenum should be as cool as possible to prevent heating of the suction gases which would lower the efficiency of the compressor. Furthermore, the suction plenum should be as large as possible so as to allow a minimum of pressure drop on the suction stroke of the compressor by providing the maximum volume of refrigerant gas available adjacent the suction port and the valve plate.
It has been recognized that increased energy efficiency can be obtained by making a suction muffler from a plastic material and mounting it as close to the suction plenum as possible. One such arrangement is shown in the present inventor's U.S. Pat. No. 4,401,418 assigned to the assignee of the present application. However, with the arrangement shown in that patent, it is still necessary to use a one piece cylinder head having the discharge and suction plenums formed integrally therein and separated by an internal wall. With this arrangement, the walls of the suction chamber, because of the high conductivity of the metal cylinder head, tend to allow a certain amount of heating of the suction gases within the plenum chamber.
One effort to overcome this seating is shown in U.S. Pat. No. 4,573,881 in which a tube formed of plastic material having a low thermal is mounted as a liner within the suction plenum and connects directly from the suction muffler chamber to the suction port in the valve plate. However, such an arrangement loses the advantage of the plenum chamber and may present difficulties on assembly of the compressor.
Another arrangement to reduce the heating of the suction gases is shown in U.S. Pat. No. 4,573,880. In this patent, a suction plenum is eliminated completely and a tube extends directly from the suction muffler into the suction port on the valve plate thereby completely eliminating the suction plenum. Thus, while heating of the suction gases is reduced, efficiency is also lost by the restrictions on flow at the suction port because of the lack of an immediately adjacent plenum chamber.